Various efforts have hitherto been made to increase the functionality of polymeric compounds. For example, in one approach currently used to increase the refractive index of polymeric compounds, aromatic rings, halogen atoms or sulfur atoms are introduced onto the compounds. Of such compounds, episulfide polymeric compounds and thiourethane polymeric compounds, both of which have sulfur atoms introduced thereon, are in practical use today as high-refractive index lenses for eyeglasses.
The most effective way to achieve even higher refractive indices in polymeric compounds is known to involve the use of inorganic metal oxides.
For example, a method for increasing the refractive index by using a hybrid material composed of a siloxane polymer mixed with a material containing small dispersed particles of zirconia, titania or the like has been disclosed (Patent Document 1).
A method in which a condensed ring skeleton having a high refractive index is introduced onto portions of a siloxane polymer has also been disclosed (Patent Document 2).
In addition, numerous attempts have been made to impart heat resistance to polymeric compounds. Specifically, it is well known that the heat resistance of polymeric compounds can be improved by introducing aromatic rings. For example, polyarylene copolymers with substituted arylene recurring units on the backbone have been disclosed (Patent Document 3). Such polymeric compounds show promise primarily in use as heat-resistant plastics.
Melamine resins are familiar as triazine resins, but have a very low decomposition temperature compared with heat-resistant materials such as graphite.
The heat-resistant organic materials composed of carbon and nitrogen that have been in use up until now are for the most part aromatic polyimides and aromatic polyamides. However, because these materials have straight-chain structures, their heat-resistance temperatures are not all that high.
Triazine-based condensation materials have also been reported as nitrogen-containing polymeric materials having heat resistance (Patent Document 4).
In recent years, there has arisen a need for high-performance polymeric materials in the development of electronic devices such as liquid-crystal displays, organic electroluminescent (EL) displays, optical semiconductor (LED) devices, solid-state image sensors, organic thin-film solar cells, dye-sensitized solar cells and organic thin-film transistors (TFT).
The specific properties desired in such polymeric materials include (1) heat resistance, (2) transparency, (3) high refractive index, (4) high solubility, and (5) low volume shrinkage.